1. Field of the Invention
This invention relates to a method of manufacturing optical elements such as lens, diffraction gratings, and prisms having high-accuracy configuration and to molds for molding such elements.
2. Description of Conventional Examples
Conventional methods of manufacturing diffraction gratings are as follows: (1) An aluminum film formed on a glass substrate is processed by pressing by means of a superfine ruling engine into a matrix, the matrix is applied with a release agent and provided thereon with an aluminum film as a reflection film by vacuum deposition, a glass substrate is adhered to the aluminum film with an adhesive, and, after the adhesive has been cured, the glass substrate with the aluminum film adhered thereto is pealed off the matrix, thereby to obtain a replica diffraction grating. (2) A resist is applied on a glass substrate and subjected to hologram exposure to form a sinusoidal relief, and a reflection film is formed thereon to obtain a diffraction grating. (3) A glass substrate is coated with a resist having an etching rate higher than that of a mask resist, and the mask resist is formed thereon. Then, a relief grating which serves as a mask against ion beam is formed thereon, and an original board is produced by removal of the mask resist and a part of the resist under it by use of an ion beam. Then, after preparation of a matrix therefrom by electroforming, a replica diffraction grating is made by the same technique as in (1). (4) A matrix is formed by electron beam drawing to prepare elements by replica. (References: A Japanese article entitled "Variety of Techniques Applied to Resin Optical Parts for Realizing .mu.m-Order 3-Dimensional Shapes", NIKKEI MECHANICAL June 17, 1985, pp. 85-94; A Japanese article entitled "Ion-Etched Blazed Holographic Zone Plates" by Y. Ono et al, papers of The 12th Micro Optics Seminar, pp. 6-10; Japanese Laid-Open Patent Application No. 59-65810/1984; A Japanese article entitled "Production of an Objective Lens for CD Using a Micro-Fresnel Lens", Extended Abstracts of The 33rd Spring Meeting, 1986, The Japan Society of Applied Physics and Related Societies, p. 113, 3a-H-3)
However, diffraction gratings prepared by the above methods always have a composition of a glass substrate, adhesive layer of resin, and a reflection layer, and are susceptible to temperature or humidity changes. In addition, the life of the matrix for preparing replica is unsatisfactory in view of mass production for supplying inexpensive diffraction gratings.
In micro-Fresnel lens preparation also, elements were made so far by carving in saw teeth gratings on an acrylic sheet one by one by machining, leading to only low properties of optical elements and to problems in properties of optical elements against temperature and humidity changes and in mass production properties. (Reference: A Japanese article entitled "Micro Optical Element for an Optical Disk", Extended Abstracts of The 33rd Spring Meeting, 1986, The Japan Society of Applied Physics and Related Societies, p. 121, 3p-A-8)